FR2467246A1 - METHOD FOR CONTROLLING THE CORROSION OF METAL SURFACES IN A BOILER SYSTEM - Google Patents

Abstract

The invention relates to a method for controlling corrosion of metal surfaces in a boiler system due to oxygen dissolved in water. According to the invention, there is added to this system an effective amount, from 0.1 to 20 parts by weight per part of oxygen in water, of an oxygen scavenger selected from the group consisting : (CF DRAWING IN BOPI) wherein R and R1 are independently selected from the group consisting of -OH or -NH2; R2 (when present) is lower alkyl containing 1 to 8 carbon atoms; M is H, Na or K; and their combinations. The invention applies in particular to the treatment of boiler feed water.

Description

The present invention relates to a method for retarding the

  corrosion in boiler feedwater systems due to dissolved oxygen

  adding to the boiler water as a purifying agent

  oxygen, hydroquinone or certain derivatives thereof. The present invention is intended for use in any water system of a boiler, for example at pressures of the order of 0 to 68.6 bar or more. Metal surfaces exposed to these conditions

  are usually made of iron and steel.

  In boiler systems, corrosion can occur in supply lines,

  heaters, economizers, boilers,

  Steam and return iron and steel. Oxygen dissolved in water is a major factor influencing the corrosion of these metals. Control of the problem of the presence of oxygen in boiler systems, particularly in the feed water section, by conventional oxygen scavengers, sodium sulfite or hydrazine, is not readily available. is not completely satisfactory, because they are not very efficient at

low temperatures.

  Thus, although a number of oxygen scavengers are known to control corrosion in boiler water systems, they are not

  are not entirely satisfactory.

  It has now been found that by practicing the present invention, a new method for the control of corrosion in boiler water systems and other aqueous systems is obtained.

  overcome many disadvantages of the prior art.

  The oxygen scavengers (additives) contemplated in the present invention are o- or p-dihydroxy, diamino and aminohydroxy benzenes and their lower alkyl substituted derivatives, i.e.

R R

lR2) ot 2 o_4 (R2)

R1 R

Q (So3M) o_2 Q Q (So3M) 0-2

0 (S03M) 0-2

R1

  R 2 or R 3 (SO 3 M) 0 - R 2 and R 1 are independently selected from -OH or -NH 2 R 2 (when present is one or more low molecular weight alkyl groups, where the alkyl group has from 1 to 8 atoms carbon, M is H, Na or K or their permutations.

  These additives can be added to the feed water

  in an amount effective to the amount of oxygen present, to maintain a small residual amount of the additive at the point of entry into the boiler. The amount fed should be from 0.1 to 20, preferably from 1 to 5 times the oxygen concentration, on a weight basis and the residual amount is generally

0.1 to 1 part per million.

  The ability of hydroquinone to react with oxygen has been known for a long time. One can for example

  refer to Green and Branch, J.A.C.S. 63, 3441 (1941).

  Quinone is taught as a catalyst for hydrazine in cleaning or purifying oxygen in the patent

  U.S. No. 3,551,349. The description mentions hydroquinone.

  U.S. Patent No. 4,096,090 teaches the use of hydroxyamines or ortho disubstituted diphenols as part of the catalyst system for catalyzing the reaction between oxygen and hydrazine. By the same inventor, U.S. Patent No. 4,026,664 covers a similar type of invention. U.S. Patent No. 3,843,547 teaches the use essentially of the same types of ortho or para-dihydroxyamine and diamino compounds covered by

  this description, but simply as catalysts,

  present in small quantities, for the hydrazine-

  oxygen. US Patent No. 1,988,823 also teaches the use of hydroquinone as part of a rust removal composition for pocketing attack on copper, brass, aluminum or welds. as it is known, none of the compounds of the class described herein has ever been used before to purify oxygen in boiler water

  or in other closed aqueous systems.

  In the present description, feedwater

  boiler, boiler water and boiler water system signify water in the boiler system plus minor amounts of salts and air and / or oxygen

  dissolved, resulting from the use of commercial waters

  in boiler systems. Such systems may also contain small amounts of additives normally used for the control of corrosion, scale, sedimentation, pH, hardness and

  like. In the present invention, the addition of

  addition of the additive to the feed water system in

  as early as possible in the system.

  The practice of the invention will become more apparent on reading the non-limiting examples which follow.

EXAMPLE 1

  The following laboratory experimental work shows that above pH 8.5, hydroquinone is an effective deoxygenating agent for water at room temperature (200C). The speed of the reaction is mitigated by a higher pH and temperature. No

catalyst is necessary.

  Tests were carried out in a 2-liter oxygen cylinder with agitator and oxygen electrode at room temperature. The results are compared with those given by sodium sulfite, and hydrazine. Oxygen residues as a function of time are shown in the table. The results with hydroquinone are very favorable when compared with those given by other oxygen scavengers. In addition, there is no accumulation of dissolved salts with sulfite, and hydroquinone is well

cheaper than hydrazine.

BOARD

  Dissolved oxygen concentration This use

EXAMPLE 2

example gives a process

of the invention.

  recommended for one The boiler used is a CleaverBrooks boiler, water tube, model S-WTHP-7A-1250 series Time minutes Na2S03 Hydroquinone N2H4 76 ppm 5 ppm 10 ppm 20 ppm 10 ppm

0 8.75 8.85 8.85 8.80 8.40

I 6.40 4.15 0.50 0.20

2.70 3.90 0.12 0.02 -

3 3.50 t 3.78 0.11 0.00

4 | 2.60 3.70 0.10 0.00 -

1.95 3.60 0.10 0.00 -

0.48 3.15 0.05 0.00 -

0.15 2.82 0.00 0.00 -

0,00 2,20 0,00 0,00 8,00

24 hr 0.00 1.00 0.00 0.00 3.05

2467246,

  335, producing 68.1 kg of steam under pressure, capacity 221,760 Cal / h, equivalent power: 20.12 KW. The

  capacity of the water supply pump is 68.13 l / h.

  The water used is partly a recycled condensate and partly the make-up water of a deep well. A 5% aqueous solution of hydroquinone and enough alkali are added to bring the pH to 8.5 to 11 and pumped into the water supply line. The amount used depends on the amount of oxygen in the feed water. The goal is to provide sufficient hydroquinone and alkali to maintain at least 0.1 to 1 ppm of residual hydroquinone in the boiler water, while maintaining the pH at over 8.5 in the water lines. 'food. The analysis of the residual hydroquinone must be done in the water of the boiler. The amount of hydroquinone supplied is adjusted to maintain the

  residual amount above in the water of the boiler.

  It has been found that hydroquinone, added to feed water at any point in the water supply system, at a pH above 8 and preferably from 8.5 to 11, reacts with oxygen. dissolved in the feed water and provided corrosion protection to the metal surfaces. The required amount is only 1 to 5 times the amount (by weight) of oxygen present, the reaction proceeds at room temperature and the only requirement is an alkaline pH greater than 8.0, the reaction

  being so much faster that the pH is higher.

  Normal water saturated with air contains 7 to 9 parts per million of oxygen according to the temperature and the atmospheric pressure. To maintain a small residual amount of hydroquinone, for water saturated with air, slightly more than 28.35 g of hydroquinone is needed for an additional 3.785 liters for water saturated with air. After purification of the oxygen, this gives a residual amount of the order of 0.1 to 1 ppm of hydroquinone. Deep waters are usually far from saturated with air, surface water can be almost saturated. The amount of hydroquinone required will be based on the amount of oxygen present and since the water will generally not be saturated with air, it will usually be considerably lower than the amount mentioned above. However, it is necessary to aim for the same residual quantity. The ratio of the weight of the additive to the weight of oxygen in the feedwater is of the order of 0.1-20: 1 and preferably of the order of 1-5: 1. The treatment can be added at any convenient point near the beginning of the feedwater treatment system. You have to add enough alkali at the same time, if necessary,

to ensure good pH levels.

  Of course, the invention is not limited to the embodiments described which have been given by way of example. In particular, it includes all the means constituting technical equivalents of the means described and their combinations if they are executed according to its spirit and implemented in

  the framework of protection as claimed.

Claims (5)

CLAIMS N E N T I N T I N G ___________________________   1. A method for controlling the corrosion of metal surfaces in a boiler system caused by oxygen dissolved in water, characterized in that it consists in adding, to said system, an effective amount of 0.1 to 20 parts by weight per part of oxygen in water, an oxygen scavenger selected from the group consisting of R R 4I.R2) (R2) 0-4 oJ 0-4- Ri R R X (S0M) 02-2 R1 R or (o) -   R 1 R or (SO 3 M) o R 2 and R 1 are independently selected from the group consisting of -OH or -NH 2; R2 (when present) is lower alkyl containing from 1 to 8 carbon atoms;   M is H, Na or K; and their combinations.   2. A process according to claim 1, characterized in that the oxygen scavenger is used in an amount between 1 and 5 times the weight of oxygen in water.   3. Process according to any one of the claims   1 or 2, characterized in that the purifying agent   oxygen is hydroquinone. 2467246-   4. A process according to claim 1, characterized   in that the pH is greater than 8.   5. Process according to any one of the claims   prior art, characterized in that the aforementioned metal surfaces are made of iron and / or steel; in that the purifying agent is hydroquinone added to the water   supply of the boiler; in that the feed water   contains dissolved oxygen; in that the amount of hydroquinone fed is 1 to 5 times the weight of oxygen in the feedwater; in that the hydroquinone in the water in the boiler is maintained at about 0.1-1 ppm; and by maintaining the pH of the feed water boiler between 8 and 11.